Polylactic acid (PLA) is a bio-degradable polymer that can be produced from lactic acid, which can be fermented from crops such as maize. This makes it an ideal candidate for use in certain energy rich, cash poor areas of the world.

It is harder then PTFE and melts at a lower temperature (around 180°C to 220°C), and a glass transition temperature between 60-65 °C, so is potentially a very useful material. It does exhibit higher friction than PTFE however which can make it difficult to extrude and more susceptible to extruder jams.

Contents

for chemists

A note from wikipedia:

The name "polylactic acid" is to be used with caution, not complying to standard nomenclatures (such as IUPAC) and potentially leading to ambiguity (PLA is not a polyacid (polyelectrolyte), but rather a polyester)

Usage

PLA is the ideal material for a Mendel RepRap. It is dimensionally stable, so there is no need for a heated bed. It is relatively inexpensive, and is not hard to source in filament form.

PLA prints nicely directly to a very lightly oiled sheet of polycarbonate/Lexan. Some tips for printing on Polycarbonate:

If you have trouble getting it to stick, try raising your extrusion temp a few degrees. At 185C I have no trouble, but at 180C it is almost impossible to get a good first layer. On large prints, bumping the print temp by 5 degrees or so can improve first layer bonding.

Use a VERY small amount of oil. Too much and it will not stick, too little and it will stick to well. I wipe a small amount of cooking oil on a a paper towel and wipe that on the surface. it should feel just slightly oily. It takes practice to get it right, but it is not hard.

Start your print a bit higher than you would expect. I do about .45-.6mm for .35mm layer height, and the prints just pop off when done.

Keep a chisel on hand just in case. If you surface isn't oily enough or you start too low, it will bond pretty tightly. You will need a chisel to remove it and scrape off the remnants. With practice you will rarely need it, but keep it on hand just in case.

No Heated build platform is necessary, and I have not tested it with one.

If you are in the US, Home Depot sells an 8x10x0.093" piece of Polycarbonate for under $4. It attaches perfectly to the existing bed of your Prusa with double sided tape. It will need to be replaced as it gets scratched up, but it will be usable for many prints, and is far less hassle than blue tape.

Home Depot also sells acrylic and clear styrene sheets for less money. They may work fine, but I have not tested. I know acrylic is not recommended without oil, but I am not sure if anyone has ever tested it with oil.

This is tested with PLA only, I have not tried it with ABS.

Moisture Issues

PLA can absorb moisture from the air. When it is heated this moisture can turn to steam bubbles which with certain hot end (extruder head) designs can interfere with printing. The symptom is that when the extruder motor stops the PLA kept coming out. When the stepper starts again there is a significant delay. Occasionally the tip may blow a bubble with a tiny puff of what looked like steam.

Small amounts of PLA filament (Natureworks PLA4043D has been tried) can have some moisture removed by putting it on a piece of aluminum foil in an oven heated to 170F for an hour. The filament in the oven is floppy, but sticks to itself only slightly. Flexing the coils after cooling unsticks them from each other. Heating a whole spool this way has not been tried, and may result in the spool becoming unusable, so caution is advised.

Interestingly, a weight change can be seen after baking. One coil went from 120.5 grams to 120.0 grams (almost 1/2%).

Color influence

It was observed that the color of the PLA (maybe the 4042D from ultimachine) seems to alter some of its properties (from multicolour prints)

Black is lovely and glossy about 75% opaque

Yellow is clean and precise when extruding at 196°C, it layer bonds very well and the printed parts feel very similar to ABS, being strong but with a little give

Black and Yellow don't snap when you bend it, unlikely for blue/green

The blue is particularly odd giving micro-bubbles inside the extruded filament if I run it at 196°C, but these are minimized at 187°C.

The blue/green is more brittle in it's filament form, but produces a very hard part when extruded.

Green filament fall between Yellow and Blue, looks really nice when printed, it seems to give the best definition of the printed object.

The Red is more 'sticky' and is a little prone to very fine strings, maybe a change in temperature will resolve this

Availability

Engineering Data

Safety

Synthesis

A crude form of PLA can be produced by simply heating powdered lactic acid with powdered stannous chloride - commonly used in pottery glazes - in a test tube. Extracting it from the test tube afterwards is left as an excercise for the diligent student.

See papers in footnote for further details.

Papers etc

[[File:PLA-kim-23-2-6-98033.pdf: Synthesis, Characterization and in Vitro Degradation of Poly(DL-Lactide)/Poly(DL-Lactide-co-Glycolide) Films.|thumb]]